Klaus-Peter Wendlandt

Treatment of boron-containing pentasil-type zeolites under ‘boron-extracting’ conditions

Thermal or hydrothermal treatments of boron-containing pentasil-type zeolites, as well as acid-leaching procedures, lead to the partial or full removal of the framework boron atoms from the material. Resulting from this removal, the boron-stimulated lattice contraction is nearly completely cancelled. Catalytic properties of the ‘deborated’ material in acid-catalysed reactions are very close to those measured on comparable boron-free samples. This fact can be utilized in the production of template-free ZSM-5 of enhanced SiO2/Al2O3 molar ratio.

Properties and applications of boron-containing pentasil type zeolites

Abstract Boron-containing zeolites of the ZSM-5 type exhibit modified structural and surface chemical properties as compared to pure aluminosilicates of similar structure. These property changes are reflected in acid catalyzed reactions in which catalysts prepared on the basis of these so-called H-SABO molecular sieves show a higher time-on-stream stability and a more advantageous product selectivity than conventional ZSM-5 containing catalysts. Some potential industrial applications for hydrocarbon conversion processes are discussed.

Organic-free synthesis, structure and properties of multicomponent ZSM-5 type zeolites

The SiO2/Al2O3 molar ratio, acidity and particle size of ZSM-5 synthesized in the absence of organic additives can be regulated simultaneously by the addition of various inorganic compounds to the synthesis mixture. The combined addition of chromium and boron leads to products in which the properties of the single systems, e.g. small zeolite particles in the chromium-containing samples and reduced acidity in the boron-containing zeolites, are reflected in a catalytically advantageous manner. This is demonstrated by the results from acid- or bifunctionally catalysed hydrocarbon conversion reactions: paraffin cracking, xylene isomerization and dehydrocyclization.

Phase and surface composition and dispersion of MoO3 in MoO3/Al2O3—SiO2 catalysts

Abstract MoO 3 /Al 2 O 3 -SiO 2 catalysts containing between 1 and 30 wt.-% MoO 3 and O and 100 wt.-% Al 2 O 3 in the support are studied by means of X-ray diffraction and X-ray photoelectron spectroscopic (XPS) techniques. In contrast to the SiO 2 support, where the X-ray pattern of the 15 wt.- % MoO 3 sample shows evidence for the formation of MoO 3 crystals, in catalysts containing alumina Al 2 (MoO 4 ) 3 formation is preferred. Al 2 (MoO 4 ) 3 formation is enhanced by increasing the content of alumina in the support and by raising the amount of MoO 3 . The XPS results show a high dispersion of MoO 3 in the alumina-rich catalysts (≥30 wt.-% Al 2 O 3 ). At lower Al 2 O 3 content the preferential formation of polylayers and microcrystals of MoO 3 takes place. On an alumina-rich carrier, an increase in the Al-to-Si ratio on the catalyst surface could be observed with increasing MoO 3 content up to 15 wt.-%.

Catalytical conversion of silicon tetrachloride to trichlorosilane. Characterization of the nickel silicalite catalyst by ferromagnetic resonance spectroscopy

The formation of nickel silicide in the reaction between nickel supported on silicalite and a gas mixture (molar ratio, H2 : SiCl4= 6 : 1) is studied. By ferromagnetic resonance (FMR) based Curie temperature measurements, it was determined that the formation of metal silicides starts at 723 K. From the signal intensity, it follows that the Si content of the silicides increases with increasing temperature from ca. 1 atom% at 723 K up to 6 atom% at 865 K. The geff values suggest the presence of two kinds of alloy containing ca. 1 atom% Si: one kind, produced at temperatures up to 723 K, forms a shell layer at the surface of the Ni metal particle, and the other, generated by decomposition of silicon-rich silicides formed at 865 K, is homogeneously alloyed over the whole particle.

Study of the ammonia–zeolite interaction in modified ZSM-5 by temperature-programmed desorption of ammonia

T.p.d. of ammonia is a useful method for investigating the surface behaviour of zeolites. By means of various experimental manipulations it is possible to separate the specific ammonia zeolite interactions in order to give a sensible assignment of the corresponding adsorption sites. The high-temperature peak near 500 °C (h-peak) characterizes acidic Bronsted sites, whereas in the low-temperature desorption range two desorption peaks may appear at ca. 275 and 325 °C (l-peak and li-peak, respectively), which are though to be due to the interaction of ammonia especially with framework aluminium (l-peak) and sodium cations in the structure (li-peak).

A simple model for the kinetic evaluation of zeolite crystallization processes

Assuming that the crystal growth is the rate-determining step of zeolite crystallization, a simple equation describing the crystallization process has been developed. The equation depends on only two or, in the case of highly distorted crystallizations, on three parameters and so it allows a rational fitting even with a small set of experimental data, as is usually obtained during routine observations of zeolite syntheses. A derivation of this model from a second-order rate low with respect to the zeolite crystals and the amorphous gel is given. Applications of the model to experimental results are demonstrated for different examples including the crystallization of silicalite-1 in a fluoride system as well as inorganic MFI syntheses in the presence of boron, iron and chromium.